Progress towards the identification and improvement of dispersive soils: A review

Dispersive soils, characterized by their poor resistance to water erosion and high sodium ion concentrations, pose a significant threat to both engineering and agricultural activities. Thus, the identification and improvement of dispersive soils are of paramount importance. There are several theories regarding the causes of soil dispersion, with the prevailing view attributing it to the expansion of the electrical double layer induced by sodium ions, which subsequently reduces the cohesion between soil particles. As a result, sodium indicators such as exchangeable sodium percentage (ESP), percentage sodium (PS), and sodium adsorption rate (SAR) are commonly employed in the identification of dispersive soils. Currently, in efforts to improve dispersive soils for both engineering and agricultural purposes, chemical and biological agents are being added to enhance the soil's erosion resistance and regulate the concentration of sodium ions. Although numerous reviews have been conducted on the identification and improvement of dispersive soils, they tend to focus on the identification methods and the types of improvers, often overlooking the applicability of identification methods, the economic costs and environmental impacts of improvers. In practical improvement, the accuracy of soil identification must be ensured first and foremost. The selection of improvers should not only prioritise efficacy but also undergo thorough analysis and evaluation from multiple perspectives. This paper, therefore, reviews the advantages and disadvantages of various identification methods and assesses the differences among improvers from economic and environmental standpoints, providing a comprehensive theoretical basis for the improvement of dispersive soils.